Talk_Leiden_November_2014

Effect of primordial non-Gaussianities on
the galaxy Far-UV LF:
implications for cosmic reionization
Jacopo Chevallard
and
M. Habouzit, G. Mamon, T. Nishimichi, S. Peirani, J. Silk
References:
• Chevallard et al., 2014 (arXiv: 1410.7768)
• Habouzit et al., 2014 (arXiv: 1407.8192)

J. Chevallard - Effect of primordial non-G on the galaxy Far-UV LF: implications for cosmic reionization
Seminar - Leiden Observatory, 26 November 2014
Outline
• Introduction: primordial non-Gaussianities in the early
Universe
• Analytic modelling of cosmic reionization
• Impact of primordial non-Gaussianities on high-z halo mass
function
• Phenomenological galaxy formation model: from halo to
galaxy stellar mass function and UV luminosity functions
• Effect of primordial non-Gaussianities on cosmic
reionization history and Thomson scattering optical depth

Introducing the work...
• CMB observations indicate initial density perturbations are
Gaussian, on scales of clusters and larger
• At smaller scales we have no constraints on the statistical
properties of initial perturbations

What is the effect of deviations from Gaussianity in the initial density
perturbations, at scales not probed by CMB observations?
• Effect on the distribution of halo masses, i.e. halo mass function?
• This will propagate to the galaxy stellar mass function and UV
luminosity function

What is the effect of deviations from Gaussianity in the initial density
perturbations, at scales not probed by CMB observations?
• Effect on the distribution of halo masses, i.e. halo mass function?
• This will propagate to the galaxy stellar mass function and UV
luminosity function
Impact on Universe reionization history !

Cosmic reionization

Cosmic reionization
• Universe after Big Bang is very hot, gas is fully ionized

Cosmic reionization
• As Universe expands, gas cools down becoming neutral

Cosmic reionization
• Gas remains neutral until first sources of photons appear:
Pop III stars, first galaxies

Cosmic reionization
• Bubbles of ionized gas start to grow around early galaxies

Cosmic reionization
• Bubbles of ionized gas start to grow around early galaxies
• By redshift ~6 gas (hydrogen) is fully (re)ionized

Cosmic reionization: modeling (1)
dQHII
dt
=
˙nion
hnHi
QHII
trec

dQHII
dt
=
˙nion
hnHi
QHII
trec
Variation of volume
fraction of ionized H = # ionizations
per second
# recombinations
per second

Depends on “clumping
factor” (accounts for
inhomogeneous
temperature, density ad
ionization fields)
dQHII
dt
=
˙nion
hnHi
QHII
trec
Variation of volume
per second
# recombinations
per second

inhomogeneous
ionization fields)
dQHII
dt
=
˙nion
hnHi
QHII
trec
Variation of volume
per second
# recombinations
per second
Depends on production
rate and escape fraction
of ionizing photons

inhomogeneous
ionization fields)
dQHII
dt
=
˙nion
hnHi
QHII
trec
Variation of volume
per second
# recombinations
per second
Depends on production
rate and escape fraction
of ionizing photons
Production rate depends
on galaxy emissivity of
ionizing photons and
galaxy luminosity density

dQHII
dt
=
˙nion
hnHi
QHII
trec

H-ionizing photons per unit
UV luminosity
(from population synthesis code)
Galaxy UV luminosity density
(from integral of galaxy UV
luminosity function)
˙nion / ⇢UV ⇠ion

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM
Critical: which is the minimum UV
luminosity of a galaxy?

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM
}
e.g. Schechter function
⇤(M) / 10 0.4 ⇥M(1+ )
exp( 10 0.4 ⇥M
)

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM
}
UV LF depends on build up of
stellar mass and metals in
galaxies, hence on hierarchical
growth of dark-matter haloes

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM
}
DM haloes growth depends
on statistical properties of
initial density perturbations
(e.g. Gaussian vs non-Gaussian)

UV luminosity
⇢UV =
Z Mlim
UV
1
(M)L(M)dM
}
DM haloes growth depends
on statistical properties of
initial density perturbations
(e.g. Gaussian vs non-Gaussian)
dQHII
dt
=
˙nion
hnHi
QHII
trec

High-z galaxy UV luminosity function
• Deep, pencil-beam surveys can probe the UV LF up to z ~ 8
• At higher redshift low statistics, i.e. large errors
• To model reionization need UV LF up to z ~ 15
Bouwens et al., 2014
z ~ 4 5991
z ~ 5 3391
z ~ 6 940
z ~ 7 598
z ~ 8 225

Halo mass function

• Assuming paradigm, we run a set of N-body (i.e. “dark-matter only”)
simulations from z = 200 to z = 6.5
⇤CDM
Halo mass function

• Simulations run with Gaussian and (scale-dependent) non-Gaussian
initial conditions
⇤CDM
Halo mass function
Strongernon-Gaussianity
non G-1
non G-2
non G-3
non G-4

initial conditions
⇤CDM
Halo mass function

initial conditions
• We identify haloes and build merger trees (see Habouzit et al., 2014),
and obtain the evolution of halo mass function at 7 < z < 14
⇤CDM
Halo mass function
0.0
0.2
0.4
0.6
z =14
z =12
z =10
z = 9
z = 8
z = 7
(a)non-G 1 (b)non-G 2
9 10 11
0.0
0.2
0.4
0.6
(c)non-G 3
9 10 11
(d)non-G 4
log Mhalo [ M⊙ ]
logφnon-G−logφG[Mpc3
M−1
⊙]
Morehaloesinnon-Gsims
non G-1 non G-2
non G-3 non G-4

From halo to stellar mass function…

Merger trees

Merger trees
Phenomenological galaxy formation model (matching observed UV LF at z
= 7 and 8) + chemical evolution (mass-metallicity relation for dwarf)
dMvir
dt

Merger trees
Phenomenological galaxy formation model (matching observed UV LF at z
= 7 and 8) + chemical evolution (mass-metallicity relation for dwarf)
dMvir
dt
Large catalogue of star formation and chemical enrichment histories
dM?
dt
dZ
dt

Merger trees
dMvir
dt
dM?
dt
dZ
dt
0.0
0.2
0.4
0.6
z =14
z =12
z =10
z =9
z =8
z =7
(a)non-G 1 (b)non-G 2
7 8 9
0.0
0.2
0.4
0.6
(c)non-G 3
7 8 9
(d)non-G 4
logM∗ [ M⊙ ]
logφnon-G−logφG[Mpc3
M−1
⊙]
non G-2non G-1
non G-3 non G-4
Morehaloesinnon-Gsims

…and to Far-UV luminosity function
Catalogue of star formation and chemical enrichment histories
BC03 population synthesis code
+

Predicted galaxy UV LF at 7 < z < 14 ,
for G and non-G initial conditions
+

Predicted galaxy UV LF at 7 < z < 14 ,
for G and non-G initial conditions
• Simple (3 parameters) galaxy
formation model able to match
observed LF at z = 7 and 8
• Prediction for the evolution of the
faint-end slope with redshift also
agree with observations
+

Effect of non-G on galaxy Far-UV LF

Recall...

Effect of initial non-Gaussianity
on UV LF:
• increase with increasing
redshift (at fixed luminosity)
• increase with decreasing UV
luminosity, i.e. with
decreasing galaxy mass (at
fixed redshift)
• increase with increasing level
of initial non-Gaussianity, i.e.
increases from model non-G 1
to non-G 4

Reionization models
• Calibrated from state-of-the-art hydrodynamic simulations
• 3 different models, in which we vary escape fraction and minimum UV magnitude
Reionization model
A 0.2 -12
B
0.17 at z = 7
0.75 at z = 14 -12
C
0.17 at z = 7
0.75 at z = 14
-7
fesc Mlim
UV

Reionization models
• Calibrated from state-of-the-art hydrodynamic simulations
• 3 different models, in which we vary escape fraction and minimum UV magnitude
Reionization model
A 0.2 -12
B
0.17 at z = 7
0.75 at z = 14 -12
C
0.17 at z = 7
0.75 at z = 14
-7
fesc Mlim
UV
Increased contribution of low-mass galaxies to
ionizing budget
A CB

Impact of primordial non-G on reionization
6 8 10 12 14
0.00
0.25
0.50
0.75
1.00 G
non-G 1
non-G 2
non-G 3
non-G 4
Model A
Model B
Model C
z
QHII
Model
A 0.2 -12
B
0.17 at z = 7
0.75 at z = 14
-12
C
0.17 at z = 7
0.75 at z = 14
-7
fesc Mlim
UV
• assuming constant , only non-G 4 model differs significantly from Gaussian
• assuming increasing with z (as found in most recent hydro simulations), effect of
non-G is boosted, since effect of non-G increases with z
• lowering minimum galaxy luminosity also boosts the effect of non-Gaussianity,
as non-G (in our model) are stronger at small scales, i.e. low-masses
fesc
fesc

...and on Thomson scattering optical depth
6 8 10 12 14
0.00
0.04
0.08
0.12
G
non-G 1
non-G 2
non-G 3
non-G 4
Model A
Model B
Model C
z
τe
• as in previous plot, small
differences in for constant
(only non-G 4 model differs from G)
• increasing with z boosts effect
of non-Gaussianity (~12 % difference
among non-G 4 and G)
• lowering minimum UV
luminosity (as suggested by state-of-
the-art hydro simulations) also
boosts the effect of non-
Gaussianity, as it increases the
‘weight’ to reionization of low-
galaxies, those most affected by
initial non-Gaussianity
⌧e fesc
fesc

Conclusions (and caveats!) (1)

• (Large) initial non-Gaussianity on scales not probed by CMB affect
hierarchical growth of DM haloes (see also Habouzit et al., 2014)

• By adopting a simple galaxy formation model we can propagate this
effect to galaxy stellar mass function and UV luminosity function

• By adopting a simple galaxy formation model we can propagate this
effect to galaxy stellar mass function and UV luminosity function
• Simple galaxy formation model allows us to match observed UV LF
at z = 7 and 8, and redshift evolution of faint-end slope

• Universe reionization history affected by initial non-Gaussianity,
but currently large uncertainty from reionization physics

• Impact of non-Gaussianity on depends on escape fraction and
min. UV luminosity
⌧e

min. UV luminosity
• Adopting and from state-of-the-art hydro simulations
boosts the effect of initial non-G on
⌧e
fesc Mlim
UV
⌧e

min. UV luminosity
• Adopting and from state-of-the-art hydro simulations
boosts the effect of initial non-G on
• Potential future use of to constrain statistical properties of
initial density perturbations (if uncertainties of reionization physics
are reduced)
⌧e
fesc Mlim
UV
⌧e
⌧e

Talk_Leiden_November_2014

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